1993 Suzuki RF 600 R "parts confidence fitness 2" Questions

how to remove and replace the throttle grip on a motorcycle I need to remove the whole throttle hand grip because end part broken. I have purchased a new one. The cable is okay. how do I get this off,

...parts fittef --as I'm stuck with this service shop for the next 3 years, my confidence in Yamaha is SHAKEN--what action a0 will you take . b) what was the cause of FAILURE of the bike within 2370Km ...